JP5398546B2 - Method for producing diphenylmethanediamine - Google Patents

Description

  Methods for producing diphenylmethanediamine (MDA) by the reaction of aniline and formaldehyde in the presence of an acid are known and widely described in the literature. In practice, the diphenylmethanediamine thus produced is usually obtained as a mixture with more highly condensed polyphenylenepolymethylenepolyamines. Hereinafter, MDA refers to a mixture of bicyclic diphenylmethane diamine and more highly condensed polyphenylene polymethylene polyamines.

  Industrially, MDA is mostly converted to diphenylmethane diisocyanate (MDI) by reaction with phosgene.

  In some applications, pure bicyclic MDA may be used, for example, as a crosslinker for plastics and paints.

  In industry, MDA is produced by the reaction of aniline and formaldehyde in the presence of an acid, as described in the literature. In particular, hydrochloric acid is used as the acid. This type of method is well known and is described, for example, in “Kunststoffhandbuch, Vol. 7, Polyurethane, Carl Hanser Verlag, Munich, Vienna, 3rd edition, 1993, pp. 76-86” and also numerous patent documents. (WO99 / 40059 is an example).

  Under certain requirements, the fraction of bicyclic products in MDA can be adjusted by changing the ratio of acid to aniline and formaldehyde to aniline.

  One problem associated with MDA production is neutralization. On the other hand, conventional neutralization with aqueous sodium hydroxide is expensive. On the other hand, the salt water produced by the above procedure must be treated as waste water at high cost.

  One possibility to overcome these problems is the use of multiple dissimilar acidic catalysts. For example, WO 01/58847 describes a method for producing MDA by reacting aniline with formaldehyde in a molar ratio of 1.7-100 in the presence of a solid inorganic acidic catalyst. The disadvantages of the method described in the publication are the poor service life of the catalyst as a result of deactivation due to oligomer fouling, the presence of N-methylamines present in the aniline or formed during the reaction. Examples thereof include titration of acidic groups of the catalyst with such secondary amines, and high cost based on catalyst high cost and (reaction) downtime due to catalyst conversion and regeneration.

  WO2005 / 007613 describes a method for producing MDA in which an acidic catalyst is removed with an adsorbent. After regeneration, the acid is recovered from the adsorbent and can be used again. The disadvantage of this method is that the useful life of the adsorbent is shortened as a result of surface fouling.

  The use of other metals, especially alkaline earth metal oxides and / or hydroxides, for the purpose of neutralizing the reaction mixture, often fails because of the concomitant increase in solid formation leading to equipment collapse. It was.

WO01 / 58847A1 WO2005 / 007613A1

Kunststoffhandbuch, Vol. 7, Polyurethane, Carl Hanser Verlag, Munich, Vienna, 3rd edition, 1993, pages 76-86

  An object of the present invention is to provide a method for producing MDA that is simple, inexpensive, and capable of reliably separating an acidic catalyst in operation without causing defects in the production method itself.

  This object was surprisingly achieved by using ammonia recovered as a neutralizing agent in a further step by treatment with an alkaline earth metal oxide or hydroxide.

The present invention provides a method for producing diphenylmethanediamine, and includes the following steps.
a) reacting aniline with formaldehyde in the presence of acid,
b) neutralize the acid with ammonia;
c) separating the reaction mixture from step b) into an aqueous phase and an organic phase;
d) treating the aqueous phase obtained in step c) with an alkaline earth metal oxide or hydroxide;
e) The ammonia obtained in step d) is removed.

  The acid used is preferably an inorganic acid, more particularly hydrochloric acid.

  As a rule, alkaline earth metal oxides or hydroxides can be used in step d). Calcium oxide and / or calcium hydroxide may be used because they are readily available, primarily without problems in handling, and the resulting by-products can be disposed of.

  The process for producing MDA in step a) is performed by the reaction of aniline and formaldehyde in the presence of an acid as a catalyst as described above. This type of method is well known, for example in “Kunststoffhandbuch, Vol. 7, Polyurethane, Carl Hanser Verlag, Munich, Vienna, 3rd edition, 1993, pp. 76-86” and also in many patent documents (WO99 / 40059). Is an example).

  At least one formaldehyde donor compound can also be used instead of formaldehyde or in a mixture with formaldehyde. Formaldehyde is used in more detail in the form of formalin aqueous solution, formalin alcohol solution, hemiacetal, primary amine methyleneamine, primary or secondary amine N, N'-methylenediamine and / or paraformaldehyde. The

  The process of the invention can be carried out continuously, semi-continuously or batchwise, but is preferably continuous or semi-continuous.

  In the continuous mode, the reactants are weighed into the reactor at the desired ratio with respect to each other, and a large amount of reaction product in an amount equal to the incoming stream is removed from the reactor. An example of a reactor used is a tubular reactor. In the case of a batch or semi-continuous process, the reactants are weighed into the batch reactor, preferably fed with stirring and / or with pump circulation, and the fully reacted reaction product is removed from the reactor. Removed and sent for post-processing.

  The inventive process is preferably carried out in a molar ratio of aniline to formaldehyde of preferably 2 times or more. The molar ratio of acid to aniline is preferably greater than 0.05. These ratios increase the formation of the respective bicyclic product in the reaction mixture.

  The reaction is preferably carried out in the temperature range of 0-200 ° C, more preferably 20-150 ° C, particularly preferably 40-120 ° C. As the temperature increased, the 2,2'-isomer and 2,4'-isomer fractions increased in the reaction product.

  The pressure during the reaction is 0,1-50 bar (absolute pressure), preferably 1-10 bar (absolute pressure).

  In the case of batch and semi-continuous operation, the reaction mixture can also be subjected to so-called “aging” after all the reactants have been weighed. For that purpose, the reaction mixture is left in the reactor or is transported to another reactor, preferably a stirred reactor. The temperature of the reaction mixture at this stage is preferably above 75 ° C, more preferably in the range of 110-150 ° C.

  After the production method of step a), the reaction mixture is neutralized (step b)). For this purpose, ammonia is added to the reaction mixture. Ammonia may be supplied to the reaction mixture in gaseous form, may be saturated with water if necessary, may be in the form of an aqueous ammonia solution, or may be in the form of a mixture of both phases. The combination of ammonia and the reaction mixture occurs in a suitable apparatus such as a stirred tank, a tube (with or without a static mixing element) or other apparatus, among others. The addition of basic ammonia results in neutralization of the reaction mixture and the formation of two immiscible phases, an aqueous phase and an organic phase. Neutralization takes place at an average temperature of 40-120 ° C under a pressure of 1-10 bar (absolute pressure).

  The mixture from step b) is now in the organic and aqueous phase as described. In step c) these phases are separated. The phases are separated from one another, for example by means of decanting. Each phase is then subjected to post-treatment separately.

  An aqueous phase consisting essentially of water and an ammonium salt of an acidic catalyst dissolved in water, as well as a small amount of aniline and formaldehyde reactants and a small amount of MDA final product, in step d) are alkaline earth metals. With the oxide and / or hydroxide. As mentioned above, it is also preferred to use the corresponding compound calcium (generally milky lime or slaked lime). Ammonium salts are decomposed with the formation of ammonia. This treatment step is known as a step in the Solvay process for producing sodium carbonate. Ammonia is preferably separated with steam or inert gas by distillation or stripping.

  If necessary, if the gaseous phase rich in ammonia is concentrated and purified through further steps such as drying by adsorption or removal of vapors by condensation, they are sent to neutralization (step b)) again. Can do.

  In one embodiment, the vapor containing gas passes over calcium oxide (also called quicklime). This treatment dries the gas and converts quicklime into calcium hydroxide. It is known as slaked lime that is supplied to the process of decomposition of the ammonia salt in step d).

  Following concentration and purification, if necessary, the liquid phase containing the low concentration of ammonia remaining after the ammonia is removed is disposed of as waste water.

  The organic phase separated in step c), which is predominantly MDA and contains the residual water, ammonia and products used for the production of MDA, is worked up in the same way. This can be accomplished, for example, by a single or repeated water wash, or preferably by a combined distillation, for example for the purpose of removing aniline and water.

  MDA produced by the process of the present invention is typically reacted with phosgene to provide MDI. This type of method is well known, for example in “Kunststoffhandbuch, Vol. 7, Polyurethane, Carl Hanser Verlag, Munich, Vienna, 3rd edition, 1993, pp. 76-86” and also in many patent documents (WO99 / 40059). And WO99 / 54289 are one example).

  For that purpose, generally MDA and, if necessary, phosgene are dissolved in an inert solvent and led to the reaction. The solvent used is preferably an inert solvent, in particular an aromatic solvent such as toluene or a halogenated aromatic compound such as monochlorobenzene.

  In the above process, for example, 50-150 ° C., preferably 70-120 ° C., more preferably 70-100 ° C. in a conventional reactor such as a stirred tank, stirred tank cascade, column and / or tube reactor. Can be carried out in one or more stages at a known temperature of 0.5-10 bar, preferably 0.8-8 bar, more preferably 0.8-1.5 bar.

  By way of example, in the presence of at least one inert organic solvent, phosgene is produced by a two-stage reaction of a first phosgenation stage carried out in a static mixer and a second phosgenation stage carried out in a residence time apparatus. Can be performed.

  The crude MDI produced by phosgenation can be purified by conventional technical means such as distillation. Preferably, in the initial purification operation, phosgene and optionally the solvent can also be removed from the phosgenation reaction mixture or crude MDI, preferably substantially, more preferably completely.

  Then preferably a mixture comprising at least two of the desired monomeric MDI and / or isomers thereof, such as 2,2′-, 2,4′- and / or 4,4′-MDI, Preferably by distillation (eg pressure is 2-50 mbar, preferably 2-20 mbar, temperature is 150-250 ° C., preferably 180-230 ° C.) and / or crystallization (eg fractional recrystallization) It can then be separated by suitable technical means.

  In one embodiment of the process for producing MDI, the bicyclic product can be separated from the crude MDA and reacted by phosgenation of the gas phase as described in EP570799. And for example, provide bicyclic MDI.

  MDI produced in this way can inter alia be reacted with a compound having at least two active hydrogen atoms to form a polyurethane.

  The method of the present invention allows for cost-effective and operationally reliable MDA processing. There is no damage to the MDA. The ammonia used can be completely separated from the reaction product. The circulation of ammonia prevents product loss from occurring. The resulting aqueous salt solution is disposed of without problems.

  The following examples further illustrate the present invention.

  In an experimental apparatus equipped with a stirring mechanism, 1 kg of aniline was mixed with 0.5 kg of 30% strength by weight hydrochloric acid and the mixture was heated to 50 ° C. A total of 0.4 kg of 40% strength by weight formaldehyde solution was weighed continuously over 1 hour. The mixture was then heated to 100 ° C. and stirred at that temperature for 12 hours. During this time, aniline was reacted with formaldehyde to produce MDA.

  Thereafter, about 350 g of a 20 mass% ammonia solution at 50 ° C. was weighed into the mixture stirred vigorously for 30 minutes. The stirrer switch was then turned off. The reaction mixture was separated into an organic phase and an aqueous phase. After phase separation occurred, the phases were collected separately from the experimental apparatus.

  The recovered aqueous phase contained 18.5% strength by weight ammonium chloride.

  1 kg of the aqueous phase was mixed with 150 g of calcium hydroxide (slaked lime) in a temperature controlled laboratory apparatus. The resulting hydrated ammonia gas passed through a drying tower filled with calcium oxide and dried. The dried ammonia was used again for neutralization.

  Following complete degassing, there remained approximately 20% strength aqueous calcium chloride solution to be disposed of in the apparatus.

Claims (7)

A method for producing diphenylmethanediamine, comprising:
a) reacting aniline with formaldehyde in the presence of an acid,
b) neutralizing the acid with ammonia;
c) separating the reaction mixture from step b) into an aqueous phase and an organic phase;
d) treating the aqueous phase obtained in step c) with an alkaline earth metal oxide or hydroxide;
comprising the step of removing ammonia obtained in step e) d),
A process for producing diphenylmethanediamine, wherein the ammonia obtained in step e) is returned to step b) .   2. A process according to claim 1, wherein the acid used is an inorganic acid.   2. A process according to claim 1, wherein the acid used is hydrochloric acid.   2. The process according to claim 1, wherein the alkaline earth metal oxide or hydroxide used in step d) is calcium oxide and / or calcium hydroxide.   2. The process according to claim 1, wherein the alkaline earth metal hydroxide used in step d) is calcium hydroxide.   The process according to claim 1, wherein the organic phase obtained in step c) is purified and worked up to produce diphenylmethanediamine.   The process of claim 1, wherein the purified diphenylmethanediamine is reacted with phosphogen to produce diphenylmethane diisocyanate.